A segment is a defined set of interests, preferences, demographic properties, and so forth into which you can categorize visitors to your online channels. These sets are created using facet filters on profile data.
Calculating the number of profiles belonging to a given segment is a lot harder than it sounds, because the number of profiles can be enormous, and the facets to drill down on a segment could be complex.
How BlueConic calculates number of profiles in segments
To calculate those numbers BlueConic uses Apache Solr, which indexes the profile database and provides fast calculations of the number of profiles in a specific segment or facet. This means that whenever a profile is created or updated it needs to be indexed (again). This process of indexing new profile data can take up to 10 minutes. This is why after a profile has been updated with new values, it can take some time for these values to actually show up in the segment filters.
If you want to check your profile in real time, consult the BlueConic Simulator. The Simulator will automatically load into your page when you are logged into BlueConic in the same browser.